1. Field of the Invention
The present invention relates in general to color photography and in particular to methods useful for processing a color photographic material. More particularly, the present invention relates to a method of manufacturing a compound useful as a bleaching agent in the processing of a silver halide color photographic material.
2. Description of the Related Art
A process for developing a color photographic material generally includes a color development process and a desilvering process. In the color development process, silver halide exposed to light is reduced with a color developing agent to produce silver and, at the same time, the oxidized color developing agent is reacted with a color former (i.e., a coupler) to form a dye image. In the subsequent desilvering process, the silver produced in the color development process is oxidized with a bleaching agent and dissolved by a silver ion complexing agent commonly called a fixing agent. In general, the desilvering process typically yields a material which has less than about 10 μg/m2 of residual silver. The presence of an excessive amount of silver can lead to poor image quality. The desilvering process provides a dye image on the color light-sensitive material (i.e., a color photographic material or color photosensitive material).
The desilvering process typically includes employing a bleaching bath containing a bleach composition and a fixing bath containing a fixing agent. Alternatively or additionally, the desilvering process can include a monobath desilvering step which is carried out by using a bleach-fixing bath which contains both the bleach composition and the fixing agent.
A common process for manufacturing a bleach composition includes mixing ferric nitrate (Fe(NO3)3.9H2O), a chelating agent and ammonia. In this process, various nitrate compounds including, for example, ammonium nitrate (NH4NO3), are typically formed as by-products. The presence of an excess of such nitrate compounds can have an adverse effect on the bleaching rate of the bleach composition, such as an increase in the retention of silver in the photographic silver halide emulsion.
U.S. Pat. No. 5,093,228 discloses a (1,3-diaminopropanetetraacetato)-iron (III) complex salt which is used as a bleaching agent. This bleaching agent can provide advantages such as a high bleaching rate with fast removal of silver. However, due to the relatively high cost of the (1,3-diaminopropanetetraacetato)-iron (III) complex salt, providing a method for the economic manufacture of such compound would be beneficial.
German Patent Document No. 3,800,270 (DE '270) discloses a method for manufacturing a two-component bleaching bath concentrate using ferric bromide (FeBr3) as a reactant. The two components of the bleaching bath concentrate include a FeBr3 aqueous solution and an aqueous solution of an ammonium salt of an aminopolycarboxylic acid. DE '270 discloses that FeBr3 is stable if it is stored in a sealed bottle. The two components are mixed together to form the bleaching bath concentrate.
The method described in DE '270 has several drawbacks. For example, FeBr3 is a highly unstable compound and can decompose when exposed to air, light, heat and the like, as shown in the following equation:(air, light, heat)2FeBr3→2FeBr2+Br2.As such, the storage and transportation conditions of FeBr3 should be carefully maintained and monitored to prevent or reduce the decomposition thereof. In addition, the bleaching bath concentrate of DE '270 does not possess good stability and bleaching characteristics. Such characteristics of the DE '270 bleaching bath concentrate are discussed in greater detail below in the Examples.
In view of the foregoing, it is apparent that a need exists for a method of manufacturing a bleach composition which is cost-effective and which provides a bleach composition possessing good bleaching performance and stability characteristics.